Cardiff will allow long-serving Kevin McNaughton to leave this summer along with Danny Gabbidon and Nicky Maynard.
Highly-rated Atletico Madrid midfielder Saul Niguez has signed a new five-year contract.
Birmingham acting chairman Peter Pannu has poured cold water on claims from Gianni Paladini that a takeover deal could be agreed within the next 10 days.
Paladini's Italian-led consortium is understood to have lodged an improved £30million bid for the npower Championship club at the start of November.
Although no deal has been accepted, the Solihull-based businessman claims to be currently looking through the club's books with a view to hopefully concluding an agreement by the end of next week.
But confusion is now rife after the latest statement from Pannu, who is currently in Hong Kong along with City's Far East owner Carson Yeung.
Pannu morning told Birmingham's official website on Thursday: "There are no active negotiations with the group involving Gianni Paladini or any of his associates.
"Should there be any agreement reached, there shall be formal announcements made in Hong Kong and also in the UK. I would urge that only official information should be relied upon and not rumours or speculation."
Pannu's response comes after fresh quotes from Paladini appeared in the media last night.
The former QPR chairman, who moved from his native Italy to the midlands in the 1960s, told Telegraph Sport: "We want to get a deal done very soon because we don't want to lose any players in January. I am hopeful that we can get something agreed within the next 10 days.
"I still believe Birmingham can get into the play-offs and our intention is to sign four or five players in the transfer window to strengthen the squad.
"We have spent a lot of money trying to get this completed and are currently looking through the books. Our intentions in buying Birmingham have never wavered, we want it done, and we are keen to get it all sorted by the end of next week."
Pannu has been exploring the potential for bringing in new owners or finding investment in the club.
A first offer from Paladini's consortium, believed to be around £25m, arrived in mid-September and was rejected.
The board of Birmingham International Holdings Limited, City's parent company, duly released a statement to the Hong Kong Stock Exchange on October 9 stating they were in talks with two different unnamed parties about the possible sale of the club.
Unconfirmed reports then surfaced at the start of November that Paladini had lodged a second, improved bid in the region of £30m, placing his consortium firmly in pole position.
The bid was never announced to the Hong Kong Stock Exchange and the status of the offer remains unclear, with the quotes from Pannu and Paladini over the last 24 hours only confusing matters.
The current state of play is likely to rest somewhere in the middle of the two versions of events although a decision over the sale of the club ultimately rests with Blues' current owner Yeung, who may be holding out for improved terms.
Hong Kong businessman Yeung is currently unable to leave the Far East as he prepares for a court date later this month over alleged money laundering.